Up to now, there are known, as working fluid injection methods for a fluid dynamic pressure bearing which is used for a recording medium driving device etc., methods disclosed in, for example, Patent Documents 1 to 3.
All of the working fluid injection methods disclosed in Patent Documents 1 to 3 are vacuum injection methods. The method in Patent Document 1 is one in which: a gap between a housing and a shaft and the inside of an injecting tube are decompressed to exhaust air with the use of the injecting tube airtightly connecting with the gap between the housing and the shaft; then, an open end of the injecting tube is dipped in a liquid surface of a working fluid; and thereafter, with the release of the decompressed state in its periphery, the working fluid is sucked and injected into the injecting tube and the gap between the housing and the shaft in the decompressed state.
Further, the working fluid injection method disclosed in Patent Document 2 is one in which: a peripheral environment of a bearing unit, which is constituted of a housing and a shaft and into which a working fluid is injected, is brought into a decompressed state to exhaust air within the bearing unit; and thereafter, with the release of the decompressed state, the working fluid is injected into the decompressed bearing unit due to an atmospheric pressure.
Further, the working fluid injection method disclosed in Patent Document 3 is one in which: a bearing unit, in which an annular concave portion having the same volume as a proper amount is formed at an open end of a gap between a housing and a shaft, is brought into a decompressed state to exhaust air within the bearing unit; a working fluid is dropped to be stored in the concave portion in the decompressed state; and thereafter, with the release of the decompressed state, the working fluid stored through utilization of a differential pressure between the inside and the outside of the bearing unit is injected into the gap of the bearing unit.
Patent Document 1: JP 2002-168394 A (p. 4, FIG.1 etc.)
Patent Document 2: JP 2002-5170 A (p. 3, FIG.1 etc.)
Patent Document 3: JP 2002-174243 A (p. 3, FIG.3 etc.)